1. Field of the Invention
Apparatuses and methods consistent with the present invention are related to an energy- and time-efficient apparatus and method for drying material such as biomass, for example, firewood, split logs, and other wood mass.
2. Description of the Related Art
Many moist solid products need to be dried in an efficient way before they can be used and/or marketed. This is the case with grains and other agricultural products such as wood. Firewood and wood products dried to moisture contents below 15%, represent a unique source of high quality renewable energy with flame temperatures that exceed those of some fossil fuels.
The burning of wood is currently the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating and for fueling steam engines and steam turbines that generate electricity, as well as a myriad of other applications.
Firewood also has a number of potential uses in renewable energy technologies including as wood pellets, in efficient stoves for developing nations, and as sawdust, which can be pelletized and or used as hog fuel.
Potentially the most important step in preparing wood for use is drying. There is about 80 percent more heat value in properly dried wood (having a moisture content below about 20% ) than in freshly cut wood (having a moisture content above about 50% ) due to the lower moisture content. Broadly, there are two methods for drying timber, natural drying (or air drying) and artificial drying.
Air drying is the drying of timber by exposing it to the air. This is a simple technique generally involving putting the wood in a clean, cool, dry, and shady place, and stacking the wood to be dried such that air can properly circulate through the stack. Generally it is considered best to use wood with less than about 30% moisture content that has air dried for at least six months.
Furnace or kiln drying is a process of introducing heat to speed up the drying process.
A furnace structure may include a main body including a truncated cone or similar with a firewood charging chute at the top and guides towards the interior of the main body, as for example chain curtains hanging from a rim of an entrance opening or an inverted truncated cone to guide the wood radially outward. The main body may also be equipped with openings at the top for escaping air and moisture.
A rotary plate may be used within the main body, centered on a vertical axis of the main body. Firewood that enters the main body by the charging chute lands on this plate after its downward transit through the furnace. This plate may have pins or manual or mechanical pushers on its upper face to help the motion and circulation of the firewood. A plate having a spiral shape may also be used to help move firewood within the main body and to guide properly dried wood to an exit, where it is expelled towards a bin or conveyor belt. Additionally, other mechanical means may be used to guide dried wood to an exit of the main body.
As is described in two previous Applications of the present inventor (Uruguay Application Nos. 28,996 and 28,995, both filed on Jun. 30, 2005), the high temperature of byproduct heated chimney gas may be taken advantage of and used in the drying process.